Certain types of lifting devices are capable of both lifting heavy objects and rigidly positioning objects in three-dimensional space. For example, pneumatically assisted manually operated manipulators have found widespread use. These manipulators typically consist of an arm that extends outwardly in a generally horizontal direction from a mast about which it is permitted to rotate and from which it is also permitted to pivot arcuately in a generally vertical direction in a pneumatically assisted manner. The arm may include one or more extension members serially disposed from an end of the arm distal from the mast that are similarly permitted to rotate and/or pivot. This arrangement permits the positioning of the distal end of the arm or extension member at a desired location in three dimensional space. An end effector is an attachment coupled to the distal end of the arm or extension member and adapted for the manipulation of a desired object or for the conduct of a particular task. For example, an end effector may include clamping means, pincer means, magnetic means or the like that are shaped and/or sized for the securement of a desired object to be positioned. The manipulator normally includes a pneumatic cylinder adjusted to a pre-determined pressure selected so that the weight of the object is just balanced by the cylinder. In this manner, the object becomes weightless with respect to the operator, who is then able to manually position the object in three dimensional space.
When bending a sheet of steel using a conventional sheet metal brake, a portion of the sheet is placed within the brake and another portion of the sheet extends outwardly therefrom. The brake includes a hydraulically operated edge that fits within a complementary die located on the press. When the edge is engaged with the sheet to effect the bend, the outwardly extending portion of the sheet moves arcuately in response to bending of the sheet within the die. Conventionally, human operators hold the sheet during the bending operation and are required to follow the arcuate movement of the sheet with their arms, often ending with the operator's arms in an overhead position. This repetitive arm movement can lead to occupational strain injuries that are particularly exacerbated when heavy sheets are being bent. There is also a risk of limb loss or other accidental injury due to the proximity of the operators to the press and the potential for the operators to drop the sheet.
Although it would be desirable to utilize a pneumatically assisted manually operated manipulator in this application, currently no end effector exists that is capable of both positioning the sheet within the brake and following the arcuate movement of the sheet during the bending operation. Conventional passive end effectors are not capable of rotating or otherwise actively re-positioning the angular orientation of the sheet in order to permit successive bending operations to take place on the same sheet. What is needed is an end effector for a manipulator that is capable of both passively following the movement of the sheet and actively re-positioning the sheet. It would be desirable is this end effector were provided in combination with a suitable manipulator for working with heavy sheets.
Although conventional manipulators make the object being lifted essentially weightless, the manipulator itself requires a certain amount of human power to adjust its position. In order to manipulate heavy objects, the size of the manipulator increases as well as the size of the pneumatic cylinders. Operators are required to overcome both the inertia of the manipulator and to aid in the expression of air from the cylinders during re-positioning of the object. It would therefore be desirable to have a power assisted lifting feature on manipulators to selectively reduce the amount of manual effort required by the operator during re-positioning operations. It would be further desirable to include this power assisted lifting feature in conjunction with end effectors suitable for sheet bending operations.